Soakwells: What Are They And What You NEED To Know

Are you seeking information regarding soakwells? If so, check out the below article for helpful information regarding soakwells, covering what they are, the different types of soakwells, and a selection of frequently asked questions.

What is a soakwell?

In Australia, a soakwell is a large underground plastic or concrete tank that connects to your roof drainage system. 

Once connected, they allow water to run off your roof, into your downpipes, and down into the underground soakwell allowing the water to seep away into the surrounding soil without causing any damage to your property.

Other names for a soakwells?

There are a number of different names for a soakwell, these include:

  • Soak aways or soak holes
  • stormwater tanks
  • stormwater pits
  • drainage tanks

What are the different types of soakwells used in Western Australia?

There are a number of different types of soakwells and sizes on the market with capacities ranging from 60 litres up to hundreds of litres!

Soakwells are typically made of either polypropylene, plastic, PVC, or concrete.

Concrete Soakwells

Two concrete soakwells with lids ready for installation

More of a traditional type of soakwell, the concrete soakwell has been an industry standard for many years.  It has earnt this reputation due to its strong concrete construction and proven durability over decades of use.

Concrete soakwells come in a cylinder shape with the size varying depending on your requirements.  Concrete soakwells can also be stacked on type of each other to increase capacity.

Concrete soakwells also come with large round concrete lids that sit directly on the soakwell providing protection from overhead traffic.

Polypropylene Soakwells

A Polypropylene soakwell

Polypropylene soakwells are another great alternative to concrete soakwells.  Not to be mistaken with PVC or plastic soakwells (like the ones at bunnings), Polypropylene soakwells are a module soakwell type system that can be clicked together to suit your requirements.

Benefits of Polypropylene soakwells include:

  • Fully trafficable and suitable for installation under driveways, patios, car parks, and brick paving;
  • Can be built as big as required to meet the volume of necessary drainage;
  • Come in flat-pack form, much lighter and easier to transport compared to concrete;
  • They don’t require heavy equipment such as excavators to lift into place;

PVC (Plastic) Soakwells

PVC, aka plastic soakwells, usually come in two sides that click together and are installed with a waterproofing-type membrane surrounding it.  

PVC soakwell rapid flow with lid
A Reln rapid flow PVC soakwell with lid

These soakwells are a cheaper alternative to both concrete and polypropylene, though unlike these, they are not considered suitable for trafficable areas.

Plastic soakwells to avoid

In addition to the PVC rapid flow soakwells, you can also get another plastic type of soakwell that doesn’t have corrugated, re-enforced sides.

However, I’ve had to repair and replace and a number of these types of soakwells over the years (See top soakwell in the below photo). Therefore, if you’re going to go for a plastic soakwell then ensure it’s something like the Reln PVC soakwell with the enforced sides.

Collapsed soakwells in need of repair

What is the best soakwell to use in WA?

There are a number of factors that come into play when choosing a soakwell, however, if I was asked what soakwell I prefer then my recommendation is a polypropylene soakwell.

My reasons are as follows:

  • Light and easy to assemble;
  • Come flat packed meaning they are easy to transport;
  • unlike concrete soakwells, there is no need for a crane or excavator to lift them into place;
  • Trafficable meaning they can be installed in areas of traffic (Trafficable up to 30t/m2);
  • Unlike some plastic soakwells, they don’t collapse due to their internal rib-like structure;
  • With a much larger surface drainage area, they are efficient in drainage and can drain up to 50% faster than concrete or plastic soakwells; and
  • With their modular structure, they can be interlocked and extended either vertically or horizontally to suit your property (great for confined spaces with limited access).

Frequently Asked Questions

As a roof plumber, I often get asked a number of soakwell-related questions. To help I thought I would list answers to the most common questions I would get asked. If you have a question that isn’t covered, contact us via our online form and we’ll get back to you with the answer.

Do you have to install soakwells by law?

No, you’re not legally obliged to have soakwells installed.  However, in Western Australia, the law states that it is the owner’s legal obligation to retain stormwater within the boundaries of their property.

Why? This is to prevent stormwater runoff into roads or onto surrounding properties.  Known as ‘storm water’ pollution, if stormwater is not retained within your property it has the potential to run off elsewhere, causing soil erosion, flooding, and rain damage (particularly in urban areas).

Although soakwells are the most common way to prevent stormwater runoff there are also other ways you can do this.  One method is to install rainwater tanks that can be connected to your downpipes allowing stormwater to be collected and reused elsewhere.

Note, in areas where you have clay soils rather than sand, or high water tables, then soakwells are not suited and other solutions should be considered.

See also: Soakwell regulations in Western Australia

Can you build over soakwells?

A common question asked is whether you can build or concrete over a soakwell or whether it has to be accessible?

If you read through the different stormwater management guidelines, a common point stipulated is that soakwells installed within a concrete or paved area are to be installed with trafficable lids to ensure future access for maintenance purposes. (See the below extraction as an example)

city of claremont soakwell condition example
Source: City of Claremont, Western Australia soakwell fact sheet

Therefore, with the above in mind, it’s not recommended that you build or concrete over a soakwell, not make it inaccessible for future maintenance.

See also: Council Regulations for Soakwells in Western Australia

Can you put a soakwell under a driveway?

Yes, technically you can install a soakwell under a driveway, however, based on council guidelines it’s recommended that if installed under concrete or pavers that a soakwell is installed with a trafficable lid to ensure it can be accessed in the future.

How deep should a soakwell be?

When installing soakwells I aim for a minimum of 300m below ground with the preferred depth of 500m. Note, this is the depth from the top of the soakwell (including the lid if you have one) up to the ground. When it comes to the bottom edge of the soakwell this can vary from 800mm up to 2.4m depending on the size and type of soakwell you are installing.

How far should a soakwell be from my house?

Soakwells should be installed 1.8m from your house footings, though as always best to check this with your local council.

How many soakwells do I need?

If you have a standard house with no adjoining walls then I usually recommend one standard poly soakwell per downpipe, however, if you want to work out your exact soakwell requirements I would recommend using a soakwell calculator whilst considering soakwell guidelines and requirements specified by your local council.

How long do soakwells last?

Soakwells last for many years as long as they are maintained appropriately. As a general rule of thumb, you should aim to check your soakwells every couple of years to ensure they are working effectively.

This should involve checking that the walls of your soakwell(s) haven’t collapsed (highly unlikely) and that the soakwell has not accumulated any volumes of sand, dirt, or debris that can reduce the capacity of the soakwell. If this is the case then it’s recommended that you dig this out.

See also: Signs that you may need to replace your soakwell

Where can you buy soakwells in Perth?

There are a number of retailers, plumbing, and landscaping supply businesses that sell soakwells in Perth. These include:

It’s also worth checking out gumtree too as there are a number of listings for soakwells for sale including PVC fittings and drainage pipe to suit.

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